Managing driver fatigue: Quantifying real world performance impairment

Abstract

Driver fatigue remains a major cause of road accidents worldwide. Research has demonstrated that fatigue is comparable to alcohol in terms of performance impairment and risks to road safety. It has been well established that increased wakefulness causes driving impairment, both in simulated and on-road driving. Fatigue management systems have used simple performance tests (such as visual reaction time), in an attempt to quantify the risk of impairment to performance in the real world. Little is known however, about the relationship between such measures. The primary objectives of this study were: (1) To measure the decrements in performance caused by increasing levels of fatigue using a simple test of visual reaction time (PVT) and an interactive driving simulation task; and (2) To provide a link between simple and complex measures of performance. Secondary aims were: (a) examine the effects of fatigue on perception of performance; and (b) examine the effects of gender on fatigue, driving performance and perception thereof. Fifteen subjects (7 male, 8 female) aged 22-56 years (mean 33.6y), underwent 26 hours of supervised wakefulness (i.e. one night without sleep) before an 8 hour recovery sleep opportunity. During this time, subjects were present in the laboratory, and tested using (a) a 30-minute interactive driving simulation test, bracketed before and after by (b) a 10-minute standard PVT reaction time test. Testing periods were repeated throughout the protocol (at approx. 3, 8, 18 and 24 hours of wakefulness, and after the 8-hour recovery sleep). Extended wakefulness caused significant decrements in PVT and driving performance, as well as subjective sleepiness and perceptions of performance. While subjective measures normalised following recovery sleep, objective performance measures did not. Results suggest that although objective measures of both simple and complex performance are clearly linked, driving simulation cannot be replaced by a simple reaction time test. Gender differences were found in PVT performance and perceptions of driving ability, with females responding more slowly, and rating their driving as worse than males. Further research is needed to examine links between objective performance measures and to move closer to accurate assessments of fitness to drive. A cognitive-behavioural approach to driver fatigue countermeasures may be beneficial.